Modern pneumatic tires are constructed of a rubber-containing body and tread, and can include an inner tube or can be tubeless. Tires including an inner tube can be found on bicycles, motorcycles, and many large vehicles. Tubeless tires are used in many applications, including nearly all cars and light trucks. For both types of pneumatic tires, a volume of gas is contained within, and provides support to, the other portions of the tire. Pneumatic tires almost universally include a device that allows the tire to be inflated or deflated, thereby providing control over the volume of gas. Typically, this device is a valve stem that contains a valve and provides a point of access that is in fluid communication with the volume of gas and allows gas to be added to or removed from the tire.
Valve caps are used with valve stems and protect the valve components from dirt, water, and other contaminants. Valve caps constructed of plain black plastic are common, but other materials have been used, including metal. However, using a metal valve cap on an aluminum valve stem has proven problematic. The aluminum valve stem reacts with the metal of the valve cap, especially in the presence of humidity, leading to corrosion. It has been observed that when the valve stem and the valve cover are dissimilar metals, the corrosion process may be accelerated. Valve stem damage caused by corrosion can be severe, in some cases leading to the valve stem breaking, especially near the area of the valve stem contacting the valve cap. If a valve stem breaks, it is possible that its air containing functions could be compromised, leading to the rapid deflation of a tire.
Tire pressure monitoring systems (TPMS) have been developed for monitoring the air pressure inside pneumatic tires and can provide real-time pressure information to a driver of a vehicle having such a system. For many designs of TPMS used with tubeless tires, a pressure sensor is connected to, or is integral with, a section of the valve stem within the tire. The combination of a valve stem and a TPMS sensor may be referred to as a TPMS valve stem assembly. The sensor measures the pressure in the tire and communicates the pressure measurement to a receiver, which in turn relays pressure information to an instrument perceivable by a driver. TPMS valve stem assemblies are more susceptible to damage by corrosion than other valve stems that are not associated with a TPMS sensor because they are made of aluminum, rather than brass.
Damaged TPMS valve stem assemblies can require especially costly repairs. For TPMS valve stem assemblies that have become damaged (such as by corrosion), the tire must be disassembled and the entire TPMS valve stem assembly replaced. This is expensive, time-consuming, and inconvenient. Specifically, the tire and wheel assembly must be removed from the vehicle and the tire demounted from the wheel. Then, a new TPMS valve stem assembly is installed and the tire is remounted on the wheel and re-inflated. The tire and wheel assembly is then re-balanced and re-installed on the vehicle. Finally, the new TPMS sensor is programmed to work with the vehicle's system. And because the TPMS sensor is connected to or integral with the valve stem, the entire TPMS valve stem assembly must be replaced, even though the sensor component may be perfectly functional. Alternatively, a replacement valve stem may be installed on a TPMS rather than replacing the entire unit. However, installing a replacement valve stem still requires that the tire be removed from the wheel and the TPMS unit be removed from the wheel. Once a new stem has been installed, the TPMS and tire must be reassembled.
Thus, a need exists for improvements in addressing damaged TPMS valve stems and the costs associated with their replacement.